My Friday post talked about my reasons to split my PhD repository into many sub-repositories.  At that moment I did not really know what I was supposed to do or if git even had a command that could help me.  After walking into my office today and doing a little web searching I stumbled upon the file-branch command.  This command can filter stuff out of the git repository history.  This can mean a lot of things, but in my case it allows me to (for each sub-project I want to take out) filter out the rest of the git repository.

My PhD repository was organized in a way that each directory in the root directory contained a sub-project.  This was very convenient and allowed for a very simple command.  Lets say that in my root directory I had A, B and C; each representing a sub-project.  And I want to separate A.  The command to do this is:

git filter-branch –subdirectory-filter directory/ — –all

This command appeared in the man-page for git’s filter-branch.  It filters all the history of the project and keeps whatever you pass to the –subdirectory-filter argument.  The –all argument specifies that all the branches and tags are to be re-written.

At the end of the command I get all the contents of directory A in my root directory.  I also get only the history the pertains to the A directory.  This is awesome!!!  This is just one of the reasons why I keep faithful to git :)  Notice that all my history was also separated by projects.  That is, I did not have any commits that changed stuff in directory A and directory B.  I am not sure how git will act in those cases (It would probably do the sensible thing and ask you to edit the commit),  I wont find out as I don’t really have that problem.

Now its just a matter of organizing what is left in the root directory and voila I have successfully separated my git repository.

Note that I had to do some additional work to make a clean separation.  The git configuration file was left untouched and I had to modify it.  I used the following command to get rid of the remote references:

git remote rm origin

Then I “cleaned” the repository with the following command:

git gc –aggressive –prune=0

After these two additional commands I could continue using the “new” repository without any warnings.

For these post I followed some information posted at http://blog.fealdia.org/2010/02/20/separating-history-of-a-git-repository-subtree/.  Thanks to that rambler for all the good info :)